Plants are photosynthetic organisms able to fix inorganic carbon (CO2) in organic matter via energy from light and minerals contained in water. All carbons fixed primarily via the pentose/triose phosphate cycle are converted in numerous anabolic pathways necessary to sustain life (primary metabolism). To survive plants must adapt to their environment and synthesize an extremely wide range of organic compounds required to interact with the elements of their microenvironment (secondary metabolism). To capture the biochemical diversity of this particular kingdom both primary and secondary metabolism have to be taken into account. The primary metabolism is represented by the biosynthesis of building blocks of macromolecules such as amino acids, fatty acids, carbohydrates, and sterols.
Each of these groups of compounds is of economic importance. Fatty acids can also be used as a raw material for industrial applications in a variety of products, including soaps, lubricants, paints, detergents, adhesives, and plasticizers. Furthermore, fatty acids are the major components of edible oils. For example, fatty acid compounds are involved in building blocks for protection (cell membrane, epicuticular polymers), storage of energy in the plant seeds and as secondary messengers in the plant cell. As another example, carbohydrates are intermediates in the biosynthesis of energy reserves (starch, cellulose) and building blocks of the cell wall giving the plant shape and structure. The carbohydrates are the carbon skeletons of many biosynthetic reactions. As such, the ability to alter carbohydrate metabolism could lead to many improvements in plants, including increased transport and accumulation of starch by accumulation of hexose phosphate that could improve starch yield in the seed and the plant; alterations in the cell wall for better resistance to pest and drought; better digestibility for forage plants; and better processivity for pulp production in paper industry (e.g., less lignin and hemicellulose).
The advent of modern biology, particularly molecular biology and genetics, has opened up new avenues for altering the production of compounds of economic importance by plants. Scientists have focused on utilizing recombinant DNA (rDNA) methods, that allow new varieties of plants to be produced much faster than by conventional breeding. rDNA techniques allow the introduction of genes from distantly related species or even from different biological kingdoms into crop plants, conferring traits that provide significant agronomic advantages. Furthermore, detailed knowledge of the traits being introduced, such as cellular function and localization, can lead to less variability in offspring, and fine-tuning of secondary effects (e.g., permitting variation from what is customarily observed). After a trait has been introduced into a plant by transgenic methods, conventional breeding can be used to hybridize the transgenic line with useful varieties and elite germplasms, resulting in crops containing numerous advantageous properties.
Most efforts to engineer plants with specific traits thus far have been based on the rational design paradigm of transforming a plant with a gene of known function with the intent of introducing a known trait. As agricultural biotechnology hurtles into the genomics and post-genomics era, the massive amounts of genetic and functional data being generated are being used to direct the search for genes that can be utilized with recombinant methods. However, if the use of this information is limited to the rational design paradigm, the identification of genes with truly profound effects on the production of desired compounds by plants could be extremely time-consuming and slow.
Accordingly, what is needed in the art are methods for rapidly screening and identifying gene sequences and polypeptide sequences of previously unknown function whose expression causes altered metabolic characteristics in biological systems, including, but not limited to, plants.